Method and device for diagnosis of sensor faults for determination of angular position of polyphase rotary electrical machine

ABSTRACT

Disclosed is a method and device for diagnosis of functioning faults caused by the angular position measurement sensors of the rotor of a polyphase rotary electrical machine comprising a stator, in particular of the alternator-starter type. The diagnosis is obtained by carrying out direct measurements of pairs of sine and cosine signals determined on the basis of linear combinations of the polyphase signals provided by these sensors. This measurement therefore does not make it necessary to know the exact value of the speed of the machine. The diagnosis of functioning faults caused by the angular position measurement sensors requires only the execution of elementary logic operations, i.e. the determination of the “true” or “false” logic states of two inequality equations.

The invention relates to a method for diagnosis of functioning faults ofsensors for determination of the angular position of a polyphase rotaryelectrical machine comprising a stator.

The invention also relates to a device for implementation of a method ofthis type.

It applies more particularly to reversible machines, known asalternator-starters which are used in the automobile industry, in bothalternator and engine mode.

Within the context of the invention, the term “polyphase” relates moreparticularly to three-phase or hexaphase rotary electrical machines, butit can also relate to two-phase rotary electrical machines or machineswhich function with a larger number of phases.

For the sake of clarity, hereinafter the case of the preferredapplication of the invention will apply, i.e. the case of a three-phasereversible rotary electrical machine of the alternator-starter type,without this limiting in any way the scope of the invention.

As is well known, a reversible rotary electrical machine comprises analternator comprising:

-   -   a rotor which constitutes an inductor, which is conventionally        associated with two collector rings and two brushes by means of        which an excitation current is supplied; and    -   a polyphase stator which bears a plurality of coils or windings,        of which there are three in the embodiment considered, which        constitute an armature and are connected in the form of a star        or most often a triangle in the case of a three-phase structure,        and, in alternator functioning, provide converted electric power        to a rectifier bridge.

The alternator can also be reversible and constitute an electric motoror rotary electrical machine, which makes it possible to rotate thethermal engine of the vehicle via the rotor shaft. This reversiblealternator is known as an alternator-starter. It makes it possible totransform the mechanical energy into electrical energy, and vice versa.

Thus, in alternator mode, the alternator-starter in particular chargesthe battery of the vehicle, whereas in starter mode thealternator-starter drives the thermal engine, which is also known as theinternal combustion engine of the motor vehicle, in order to start thelatter.

In the reversible machines in the automobile industry, for example,which function according to the engine or starter modes, the current ofthe stator must be controlled so as to provide the rotor at all timeswith the torque which is necessary both to start it up and impart to itthe rotation required for the functioning of the engine. The torque tobe applied to the rotor, and therefore the current to be supplied to thephases of the stator, is a sinusoidal function of the angular position,indicated by an angle θ, of the rotor relative to the stator.

A complete system for determination of the instantaneous angularposition θ(t) of the rotor of a three-phase alternator-starter and forcontrol of this unit, both in alternator mode and in engine (starter)mode typically comprises four main sub-systems, i.e. analternator-starter, a reversible alternating-direct electric currentconverter, a module for control of this converter, and a module fordetermination of the angular position θ of the rotor.

The converter is generally constituted by an electronic rectifier bridgecomprising as many MOSFET power transistor branches are there arephases, for example three in the example described.

In alternator mode, the alternator-starter supplies the converter withthree-phase alternating current, and in engine mode it is thealternator-starter which is supplied with three-phase electrical energyby the reversible converter, which functions in three-phase currentgenerator mode.

In engine mode, the MOSFET transistors are controlled according to anappropriate sequence of six control signals which are generated by thecontrol module. As is also well-known, these signals must be generatedaccording to the angular position θ of the rotor.

It is therefore necessary to determine this angular position θ withgreat accuracy in order to obtain correct functioning of the rectifierbridges, in particular in order to prevent any risk of deterioration ofthe semi-conductor components, but also and above all, in engine orstarter mode, to obtain optimised torque provided by thealternator-starter.

This is the function which is allocated to the module for determinationof the angular position of the rotor, so as to generate a signal θ(t)which represents the instantaneous variation of the angular positionmeasured, and to transmit the signal to the input of the control module.

In the prior art, various methods have been proposed for this purpose.

By way of non-limiting example, in international patent application WO2006/010864 A2, the applicant proposed a device for determination of theposition of a rotor of a rotary electrical machine comprising a stator,which makes it possible to obtain the precise angular position required,whilst being cheap, simple to implement, and insensitive to magneticdisturbances.

The device which is taught in this patent application comprises aplurality of magnetic field measurement sensors which are fixed relativeto the stator of the rotary electrical machine, and can supply firstsignals which are representative of a rotary magnetic machine detectedby these sensors, and means for processing of these first signals by anoperator, which means can supply second signals dependent on the angularposition reached by the rotor.

The sensors are generally constituted by linear Hall-effect sensors, forexample three of them, which will be known hereinafter as S₁ to S₃,placed at 120° electrical degrees on a three-phase rotary electricalmachine, in this case an alternator-starter, opposite a target which isintegral with the rotor, and is magnetised alternately North/South foreach pole of the machine. These sensors S₁ to S₃ supply signals ofsinusoidal types VS₁ to VS₃ respectively. For a more detaileddescription, reference can advantageously be made to the description ofthe aforementioned international patent application WO 2006/010864 A2.

It has been found experimentally that the signals VS₁ to VS₃ generatedby the three measurement sensors S₁ to S₃, which will be classified as“raw”, generally comprise a high level of harmonics, and in particular asubstantial level of harmonics of the orders 3 and 5, and that theirrelative amplitudes are different. On the basis of these three veryimperfect raw signals it is therefore difficult to construct two signalswhich approximate an ideal sinusoidal function (i.e. free fromharmonics), have identical amplitudes and zero offsets, and are dephasedin a non-trivial manner (dephasing which is not a multiple of 180°).

In order to eliminate this difficulty, the basic principle is to obtaintwo distinct linear combinations which make it possible to obtain thetwo sinusoids required, whilst avoiding as far as possible theabove-described problems.

In the first approximation, it is possible to allow the sensors to havecharacteristics which are identical or at least very similar, and to beplaced in the same thermal and electromagnetic environment, andtherefore the signals which are emitted by the sensors retain commoncharacteristics. These hypotheses give reason to consider that:

-   -   their offsets develop at the same time, depending on any        disturbance field (such as, for example, the magnetisation of        the rotor);    -   their harmonic levels of the order 3 are very similar, and in        phase with their fundamental harmonics; and    -   the electric signals generated by these sensors are dephased by        approximately 120°.

These hypotheses make possible the choice of two linear combinationswhich partly cancel out the harmonic of the order 3 and the offsets. Ina simple manner, by selecting for linear combinations the differencesbetween sensor output signals, two sinusoidal signals are obtained whichare dephased by 60°, and correspond to the above-described criteria ofchoice. The signals thus obtained are re-centred and contain fewerharmonics than the raw signals.

Once the two sinusoids have been obtained, it becomes possible toextract directly the value θ of the angular position of the rotor. Forthis purpose, by dividing the two aforementioned signals, the amplitudeis dispensed with, then, by means of a mathematical function or a tableit is possible to invert the function and determine the angular quadrantby means of the signs of the signals. For the sake of clarity, by way ofnon-limiting example, if the dephasing between signals is φ=90° forexample (sine-cosine signals), this is an Arc Tangent function. Onceagain, for a more detailed description of the method, reference canadvantageously be made to the aforementioned international patentapplication WO 2006/010864 A2.

In practice, these functioning conditions, which can be classified as“ideal” are rarely fulfilled.

Consequently, again in practice, the above-described method often provesto be unsatisfactory.

Consequently, in its French patent application no. 0853359 filed on 23May 2008, the applicant proposed a method and a device for determinationof the angular position which eliminate the disadvantages of the priorart.

For this purpose, according to an essential characteristic of thismethod, the real angular position of the rotor of the rotary electricalmachine is determined by using a system for control between a realangular position and an estimated angular position. The device which istaught by this patent application comprises a feedback loop which willbe known hereinafter as a tracking loop, the behaviour of which issimilar to that of a phase lock loop or PLL.

The circuits which constitute the device for determination of theangular position of the stator are designed such that the followingequation (1) is fulfilled:

sin(θ_(real)+φ₁)·sin(θ_(est)+φ₂)·sin(θ_(real)+φ₂)·sin(θ_(real)+φ₁)=½(φ₂−φ₁)·sin(θ_(real)−θ_(est))

In this equation:

-   -   θ_(real) represents the real angular position of the rotor;    -   θ_(est) represents the estimated angular position of the rotor;        and    -   φ₁ and φ₂ represent the dephasings of the signals corresponding        to angular offsettings of the sensors relative to an angular        reference point which is associated with the stator of the        rotary electrical machine.

Consequently, φ=(φ₁ and φ₂) is a constant (these two dephasings beingdetermined by a single angular reference point), and represents thedephasing between the signals θ_(real) and θ_(est).

This equation makes it possible to obtain a signal for error between thereal angular position and the estimated angular position.

The so-called tracking loop makes it possible to minimise the errorbetween θ_(real) and θ_(est). If this error becomes slight, it is wellknown that sin(θ_(real)−θ₁) is substantially equal to(θ_(real)−θ_(est)). The second term of the aforementioned equation thenbecomes substantially equal to K(φ₁−φ₂), where K is a constant equal to½ sin(φ).

Hereinafter, for the sake of clarity, the context of a device of thistype will apply, without this limiting in any way the scope of theinvention.

It can easily been understood that the determination of the angularposition θ of the rotor relative to the stator depends on thereliability of the information provided by the measurement sensors,irrespective of the exact method implemented since, in all cases, thisangular position is obtained from a combination of the polyphase signalsprovided by these sensors.

It is therefore necessary to ensure that the sensors are functioningsatisfactorily, and to implement a method for diagnosis of functioningfaults of these sensors.

Within the context of the invention it must be understood that“measurement sensor faults” also means faults of the peripheralelectrical and electronic circuits (electrical connections, circuits forthe electrical energy supply to the sensors, etc.).

In the prior art, different diagnostic methods have been proposed.

The diagnosis of the angular position measurement sensors can beobtained by a comparison between an evaluation of the speed of thevehicle carried out by the aforementioned tracking loop, and measurementof this speed carried out by a calculation unit for example. However,the tracking loop which permits estimation of the electrical positioncan return an accurate mean speed value even when one or a plurality ofsensors has faults (such as an open circuit or a short-circuit).

FIG. 1 which is placed at the end of the present description illustratesan example of development of the speed of rotation of the rotor V,according to the time t. In this FIG. 1, a plurality of successivesensor faults have been simulated (open circuits, short-circuits, etc.),as shown by the development of the instantaneous speed V_(inst). It isfound nevertheless that the tracking loop remains locked and provides amean speed V_(moy) which is altogether correct.

Consequently, an external speed measurement is necessary in order toobtain a reference value.

Another method consists of using only the error signal of the trackingloop. However this loop is very sensitive to small saturations, andcannot detect any error in the presence of signals with a very lowamplitude (including the errors caused by short-circuits of the sensoror connectors which are disconnected). In addition, in certain-practicalembodiments, the tracking loop error signal is contaminated bysubstantial noise as the result of lack of calibration and low accuracycaused by the simplification of the electronic circuits used. Asignificant margin must therefore be allowed as far as the detectionthresholds are concerned. Consequently, a certain number of faultscannot be diagnosed. For example, simultaneous disconnection of thethree angular positioning measurement sensors or disconnection of theelectrical energy supply source is not detected.

Another method consists of obtaining the sum of the signals generated atthe output from the three measurement sensors S₁ to S₃, i.e.:

Σ=VS ₁ +VS ₂ +VS ₃≈0

However, this method makes it necessary to resort to additionalelectronic circuits such as, either to measure the signal VS₁ or tomeasure the complete sum of signals, which increases the complexity ofthe diagnostic device, and makes it more costly. In addition, for thereason previously given (low accuracy due to the lack of calibration),it is necessary to accept a substantial margin as far as the detectionthresholds are concerned. Consequently, a certain number of faultscannot be diagnosed. For example, as previously stated, thedisconnection of the three sensors or of the electrical energy supplysource is not detected.

The object of the invention is a method for diagnosis of functioningfaults caused by the angular position measurement sensors of the rotorof a polyphase rotary electrical machine comprising a stator, inparticular of the alternator-starter type, which eliminates thedisadvantages of the prior art, some of which have been indicated,without a significant increase in either the complexity of theelectronic circuits implemented, or the overall cost.

According to a main characteristic of the method according to theinvention, the diagnosis of the angular position measurement sensors forthe rotor is obtained by carrying out direct measurements of pairs ofsine and cosine signals determined on the basis of linear combinationsof the polyphase signals provided by these sensors, the acquisition of aparameter which will be known as the “speed state”, in this casetypically the states “speed>0” and “speed=0” (or also “speed≧0”), and aminimum speed profile.

This measurement therefore does not make it necessary to know the exactvalue of the speed.

According to the method of the invention, diagnosis of the main errorscaused by the angular position measurement sensors is obtained simply bydetermining the “TRUE” or “FALSE” logic states of the two equationsindicated hereinafter:

when E_(vt)>0t/mn:[(S _(pp)<TRIG_(—) PP) OR (C _(pp)<TRIG_(—) PP)];  (A)

when E_(vt)≧0t/mn:[(V _(ref) −Δ<S<V _(ref)+Δ) AND [(V _(ref) −Δ<C<V_(ref)+Δ)]  (B)

where:

-   -   E_(vt) is the speed state reached by the rotor of the        alternator-starter expressed in rpm (t/rtm)    -   “OR” and “AND” are respectively the non-exclusive disjunction        and conjunction logic operators;    -   S is the instantaneous value of the sine signal;    -   C is the instantaneous value of the cosine signal;    -   S_(pp) is the maximum peak-to-peak amplitude of the sine signal;    -   C_(pp) is the maximum peak-to-peak amplitude of the cosine        signal;    -   V_(ref) is an offset value for an analogue-digital conversion        alignment implemented in the feedback chain; and    -   TRIG_PP and Δ are two threshold values.

If the equations (A) and/or (B) are confirmed, i.e. in the “TRUE” logicstate, this state is characteristic of at least one faulty state of theangular position measurement sensors, or at least of the peripheralelectric/electronic circuits of these sensors (electrical connections,electrical energy supply, etc.) and of the magnetic target itself.

The threshold value TRIG_PP is obtained by means of the so-called“Monte-Carlo” statistical method. For this purpose, in a preliminaryphase of the method, a global mathematical model of the“alternator-starter/tracking loop” system is created, and randommodifications are applied to this model. Mathematical processing makesit possible to calculate the aforementioned threshold value TRIG_PP onthe basis of this distribution of states.

These different parameters are described and specified in greater detailhereinafter.

The invention therefore has many advantages, including the following:

The diagnosis of functioning faults caused by the angular positionmeasurement sensors requires only the execution of elementary logicoperations, i.e. the determination of the “true” or “false” logic statesof two inequations.

The parameters contained in the inequations are substantially alreadyacquired for the needs specific to the tracking loop. In particular, thetwo sign and cosine signals are necessary in order to determine thevalue θ of the angular position of the rotor. The determination of theaforementioned logic states can be obtained simply, in a preferredembodiment, by making use of one of the on-board computers present inany vehicle with a modern design.

The calculation of the values of the aforementioned threshold valuesTRIG_PP, Δ and V_(ref) is carried out during a single preliminary phase,typically during the design of the system, and does not require anyadditional circuit on board the vehicle, or even modifications ofsoftware systems implemented in the programme memories of the on-boarddigital computers.

The main object of the invention is thus a method for diagnosis offunctioning faults which exist in sensors implemented in a system formeasurement of the angular position of a rotor of a polyphase rotaryelectrical machine comprising a stator, the sensors being fixed relativeto the stator, and able to detect a magnetic field and provide firstsignals which are representative of this magnetic field, characterisedin that it comprises at least one step of generation, from linearcombinations of the said first signals, of at least one pair of firstand second sinusoidal signals, which are dephased by a predeterminedvalue different from zero and from 180°, representing an angularposition of the rotor;

a step of determination of a first parameter known as the speed stateE_(vt) of the rotor, which assumes two values E_(vt)>0 or E_(vt)≧0, astep of calculation of the following first and second equations:

−[(S _(pp)<TRIG_(—) PP) OR (C _(pp)<TRIG_(—) PP)];

−[(V _(ref) −Δ<S<V _(ref)+Δ) AND [(V _(ref) −Δ<C<V _(ref)+Δ)],

in which “OR” is the non-exclusive disjunction logic operator and “AND”is the conjunction logic operator, S_(pp) is the maximum peak-to-peakamplitude and S is the instantaneous value of the said first sinusoidalsignal, C_(pp) is the maximum peak-to-peak amplitude and C is theinstantaneous value of the said second sinusoidal signal, and TRIG_PP,V_(ref) and Δ are three predetermined threshold values;

a step, when the said speed parameter E_(vt), is greater than zero, ofdetermination of the logic state “TRUE” or “FALSE” of the said firstequation, of generation of a signal which indicates fault-freefunctioning of the said sensors when this first equation is notconfirmed, and a functioning fault of at least one of these sensors whenit is confirmed;

and a step, when the said speed state parameter E_(vt) is equal to, orgreater than zero, of determination of the logic state “TRUE” or “FALSE”of the said second equation, of generation of a signal which indicatesfault-free functioning of the said sensors when this second equation isnot confirmed, and a functioning fault of at least one of these sensorswhen it is confirmed.

The object of the invention is also a device for implementation of thismethod.

The invention will now be described in greater detail with reference tothe attached drawings, in which:

FIG. 1 is a diagram which illustrates schematically an example of acurve showing the development of the speed of rotation of the rotor of apolyphase rotary electrical machine on a time basis, and simulatingvarious faults of the angular position measurement sensors of thisrotor;

FIG. 2 illustrates schematically an embodiment of a system fordetermination of the angular position of a rotor of analternator-starter which incorporates a device for diagnosis of thefunctioning faults of the angular position measurement sensors accordingto a preferred embodiment of the invention;

FIG. 3 is a diagram showing the development on a time basis of a pair ofsignals obtained by linear combinations of the signals generated by theangular position measurement sensors of the system in FIG. 1; and

FIG. 4 is a diagram illustrating distribution of threshold valuesobtained by means of the Monte-Carlo method according to thetemperature, such as to determine threshold ranges in order to obtain anerror diagnosis when the speed of rotation of the rotor is not zero.

Hereinafter, without in any way limiting the scope of the invention,unless otherwise stated, the context of its preferred embodiment willapply, i.e. the case of a system for determination of the angularposition of a rotor of an alternator-starter which implements a systemfor control between a measured angular position and an estimated angularposition.

FIG. 2 illustrates an example of a system 1 for determination of theangular position of a rotor of an alternator-starter according to thearchitecture described in the aforementioned French patent applicationno. 0853359. It also incorporates a device 4 for diagnosis of thefunctioning faults of the angular position measurement sensors accordingto a preferred embodiment of the invention.

The alternator-starter (not illustrated in this figure) can be of a typewhich is altogether similar to the prior art, or identical. The sensorsin the block 10 are constituted for example by three Hall-effect sensorsdisposed at electrical 120° for a three-phase rotary machine. Theelectrical energy supply of these sensors 10 is symbolised by a battery100 which provides a voltage V_(cc) of, for example, +5V.

The sensors 10 provide to the output connections 101 to 103 three “raw”signals which will be known as VS₁ to VS₃, and are transmitted to amodule 20 of linear combinations and amplitude correction whichgenerates at its outputs, connections 200 and 201, two signals which aretransmitted to supplementary modules 30 and 31.

The modules 30 and 31 apply to these signals offset values which areprovided by the modules 32 and 33 respectively. The modules 32 and 33can be constituted by memory circuits which contain predetermined offsetvalues.

At the outputs 300 and 310 from the modules 30 and 31, there aretherefore two sinusoidal signals with the same amplitude which arecentred on an axis (in other words without offset), and are dephased bya non-trivial predetermined value φ, i.e. which is different from 0° orfrom 180°, and is advantageously 90°, which signals will be knownhereinafter as S_(sin) and C_(cos).

These two components, which are derived from signals measured by thesensors 10, and are formed so as to approximate sinusoidal functions asclosely as possible, are each transmitted to first inputs of multipliers50 and 51 respectively, via the connections 300 and 310. They thereforerepresent two instances of the instantaneous value of the measuredangular position of the rotor. These multipliers 50 and 51 receive atsecond inputs two components derived from the instantaneous value of anestimated angular position θ(t) via two feedback branches 8 and 9(connections 80 and 90), which will be known as the “sine feedback” and“cosine feedback” respectively. The signals output from the multipliers50 and 51 are transmitted by the connections 500 and 510 to the inputsof a subtractor 6, the output signals of which (connection 60) aretransmitted to an angular position calculation chain 7. The signalswhich are output to the connection 70 represent the instantaneous valueof the estimated angular position θ(t) and are re-injected to the secondinputs of the multipliers 50 and 51 via the aforementioned feedbackcircuits 8 and 9.

The circuits which constitute this architecture provided with a trackingloop are arranged such that the equation (1) referred to in the preambleof the present description is fulfilled.

Up to this point, the architecture of the above-described system 1 fordetermination of the angular position of a rotor of analternator-starter is common to an embodiment according to the priorart.

A description will now be given of a preferred embodiment of a device 4for diagnosis of functioning faults of sensors 10 for determination ofthe angular position of the rotor which is incorporated in this system1, and more generally in many other systems which use sensors fordetermination of the angular position of a rotor of a polyphase machine.As will be demonstrated, it is simply necessary to have at least onepair of signals obtained from linear combinations of the polyphasesignals generated by the sensors, which in itself is known, and is notspecific to the invention.

The device 4 which is specific to the invention, for diagnosis offunctioning faults of the sensors 10 for determination of the angularposition of the rotor, comprises a diagnostic module 40 itself, andmeans 41 to indicate the speed of the rotor, and more specifically aspeed state EV_(t).

In fact, as previously stated, according to an advantageouscharacteristic of the method of the invention, it is not necessary toknow the precise value of the speed, but only to distinguish between thedistinct states.

The diagnostic module 40 receives at first and second inputs e₁ and e₂the signals which are present at the outputs 300 and 301, which areknown as S_(sin) and C_(cos). The signal which represents the speedstate E_(vt) is transmitted to a third input e₃ of the module 40.

The module 40 generates as output a signal 400 which indicates thepresence or absence of sensor functioning faults, the nature of whichwill be specified hereinafter.

These three series of signals constitute the essential information whichit is necessary to know at cruising speed in order to obtain a diagnosisof the main functioning faults of the sensors for determination of theangular position of a rotor.

As previously stated, this diagnosis is obtained by determining the“TRUE” or “FALSE” logic states of the equations (A) and (B) below:

when E_(vt)>0t/mn:[(S _(pp)<TRIG_(—) PP) OR (C _(pp)<TRIG_(—) PP)];  (A)

when E_(vt)≧0t/mn:[(V _(ref) −Δ<S<V _(ref)+Δ) AND [(V _(ref) −Δ<C<V_(ref)+Δ)]  (B)

The different parameters which are given in these equations have beenspecified in the preamble of the present description, and do not need tobe explained again.

A logic state of the equations (A) and/or (B) in the “TRUE” stateindicates at least one faulty state of the Hall-effect sensors 10 or ofthe peripheral electrical/electronic circuits (electrical connections,electrical supply circuits 100, etc.).

When the equation (A) is confirmed, in other words when E_(vt)≠0 t/mn,the main faulty states diagnosed obtained are as follows (for a rotationspeed range E_(vt) going from a very small number of revolutions perminute to a high number of revolutions per minute, a single period ofrotation being sufficient to carry out the diagnosis):

-   -   S₁ short-circuited, i.e. for example connected to a potential at        0V or 5V, on the assumption that these sensors are supplied by        the electrical supply source 100: V_(cc)=+5V;    -   S₁ disconnected;    -   S₂ or S₃ short-circuited, for example at 0V, +5V or between one        another;    -   S₂ or S₃ disconnected;    -   S₁ and S₂ short-circuited, for example at 0V, +5V or between one        another;    -   S₁ and (S₂ or S₃) disconnected;    -   S₁ and S₂ and S₃ short-circuited, for example at 0V, +5V or        between one another;    -   S₁ and S₂ and S₃ disconnected;    -   electrical energy supply source 100 faulty, which in particular        includes disconnection of the source, short-circuiting to ground        (earth of the device) or short-circuiting at the voltage    -   V_(cc) (+5V in the example described);    -   detection of short-circuit impedance, typically lower than 5 KΩ,        obviously depending on different parameters associated with a        mode of practical embodiments of the device.

When the equation (B) is confirmed, including at zero speed, the mainfaulty states diagnosed obtained are as follows:

-   -   S₁ and S₂ and S₃ disconnected;    -   S₁ and S₂ and S₃ short-circuited, for example at 0V, +5V;    -   S₁ and S₂ and S₃ short-circuited, for example at 0V, +5V or        between one another;    -   electrical energy supply source 100 faulty.

Another piece of information which needs to be known is the minimumperiod of time which must elapse after starting, before a significantpeak-to-peak measurement can be made of the signals S_(sin) and C_(cos).This information depends on the speed profile which the system has.

For the sake of clarity, it will be assumed that:

${S_{\sin} = {{V\; {\sin \left( {\theta + \frac{\pi}{6}} \right)}\mspace{14mu} {and}\mspace{14mu} S_{\cos}} = {V\; {\sin \left( {\theta - \frac{\pi}{6}} \right)}}}},$

such as to obtain a complete period for the two signals S_(sin) andC_(cos), where

$\theta_{\min} = {\pi + {\frac{\pi}{6}.}}$

Again for the sake of clarity, it is assumed that a minimum speedgradient makes it possible to go from a speed of rotation of the rotorfrom 0 to 300 rpm in 0.6 seconds. In these conditions, the calculationshows that a cruising speed of 500 rpm is reached in approximately 180ms.

FIG. 3 is a diagram showing the development of the signals S_(sin) andC_(cos) on a time basis. The Y-axis (voltages V) is graduated in volts,and the X-axis (time t) is graduated in seconds. In the exampledescribed, after a transitory period, a cruising speed of t=0.1802seconds is reached.

Consequently, in the case of E_(vt)>0 (equation (A)), a significantdiagnosis can be obtained after a minimum period of time ofapproximately 180 ms.

A priori, this parameter is known once and for all for analternator-starter with given physical and electrical characteristics.It is therefore not necessary to provide particular measurement means onboard the vehicle.

The same applies for the threshold value TRIG_PP included in theequation (A), as described in the preamble of the present description.

This parameter is determined during a preliminary phase of the method, apriori once and for all during the design of a system with givenphysical and electrical characteristics.

For this purpose, in order to obtain the threshold value TRIG_PP, it ispossible to use a statistical method, for example advantageously theso-called “Monte-Carlo” algorithm. This algorithm is very general, andcan be applied to any model for which it is possible to carry out randommodifications of this model, and to associate a so-called energyvariable with each of the modifications. The theory shows that once thestationary state has been reached, the distribution of the statescorresponds to a Boltzman's distribution.

Within the context of the method according to the invention, during aninitial phase, a global mathematical model of the system “magnetictarget part of the alternator-starter-tracking loop” is created, andrandom modifications are applied to this model so as to obtain theaforementioned Boltzman's distribution of states when a stationary stateis reached. Mathematical processing makes it possible to calculate thethreshold value TRIG_PP from this distribution of states.

Two main cases arise:

-   -   The magnetic target material is insensitive or has low        sensitivity to the variations of temperature, at least in the        field of normal functioning of the system: it is then possible        to adopt a constant value for the threshold value TRIG_PP. This        is the case for example with a magnetic target material based on        rare earth.    -   The magnetic target material is sensitive to the variations of        temperature. It is then necessary to take the temperature into        account, and the function which describes the threshold is a        linear function with the form:

TRIG_(—) PP=pT+K _(s)  (2)

where p is the proportionality constant (gradient), T in ° C. and K_(s)is a constant threshold value. This is the case for example with amagnetic target material based on ferrite.

In the first case, in order to determine the instantaneous temperatureof the magnetic material, a measurement sensor or temperature estimator42 is provided, as illustrated schematically in FIG. 2. The outputsignal of this temperature measurement sensor 42 is transmitted to afourth input e₄ of the diagnostic module 40.

Although this diagnostic module has been represented in the form ofautonomous calculation circuits, i.e. with wired logic, which resolvethe two inequations (A) and provide a diagnostic signal V_(diag) asoutput, it must be understood that the calculations which are necessaryfor development of the diagnosis of satisfactory functioning ormalfunctioning can be carried out by other means. Advantageously, it ispossible in particular to resort to one of the on-board computerspresent in any vehicle with a modern design, simply by adapting theprogrammes (micro-programmes, etc) which are implemented in thiscomputer, and by providing suitable interface circuits. This embodimentdoes only a few modifications, and is neither complex nor costly. Inaddition it is highly flexible, since it is well known to personsskilled in the art that the programmes can be updated as required(corrections of bugs, addition of functions, etc.).

FIG. 4 is a diagram illustrating a distribution of threshold valuesobtained by means of the aforementioned Monte-Carlo method, according tothe temperature. The X-axis is graduated in threshold values from 0 to900, and the Y-axis is graduated in ° C., from −50 to +175° C. in theexample described, with 3,000 peak-to-peak measurements having beencarried out.

The diagram in FIG. 4 has a plurality of distinct areas, which arecharacteristic of particular functioning faults of the sensors or of theperipheral circuits of these sensors:

-   -   area Z₁: the measurement points are distributed around a        straight line with a negative gradient C₁. In this area Z₁, the        sensors 10 and/or their peripheral circuits (electrical        connections, supply circuit 100, etc.) do not have any fault.    -   area Z₃: the measurement points are distributed around a        straight line with a negative gradient C₄. In this area the        sensor S₁ has a fault, and is disconnected (circuit open).    -   area Z₄: in this area the sensor S₁ is permanently connected to        the potential V_(cc) of the supply source 100 (+5V in the        example described).    -   area Z₅: this area represents a plurality of distributions of        measurement points which interpenetrate strongly, and        characterise various functioning faults of sensors or peripheral        circuits of these sensors: sensor S₁ or sensor S₂        short-circuited to zero potential, sensor S₂ permanently        connected to the potential V_(cc) of the supply source 100 (+5V        in the example described), sensors S₁ and S₂ disconnected        (circuits open), sensors S₂ and S₃ short-circuited to zero        potential, sensors S₁ and S₂ short-circuited, or sensors S₁ and        S₂ disconnected (circuits open).    -   area Z₆: in this area the sensor S₂ is disconnected (circuit        open).

It should be noted that the frontiers between areas are not clear.Consequently, clouds of measurement points are common to two adjacentareas, in particular as far as the areas Z₄ and Z₅ are concerned.

From these various measurements, the following can be deduced:

In the case of a magnetic material which is sensitive to temperature, inorder to obtain a maximum margin for the threshold value, this thresholdvalue is made dependent on the temperature. For the sake of clarity, inthe case of the example selected, the aforementioned linear function (2)which represents the threshold value can be as follows:

TRIG_(—) PP=−0.6407×T+494.38  (3)

This curve is represented on the diagram in FIG. 4 by a straight line C₃with a negative gradient k=−0.6407, which intersects the Y-axis at thethreshold value K=494.38.

In the case of a magnetic material which is insensitive or has lowsensitivity to the variations of temperature, a constant value isadopted for the threshold value TRIG_PP. For the sake of clarity, in theexample described, if it is wished to diagnose 100% of all the sensorfaults, it is possible to select the following value: TRIG_PP=449. Byway of compromise it is possible to select a slightly lower value, onthe understanding that a few cases of disconnection of S₁ may not bedetected, for example. In this hypothesis, in the example described, itis possible to select following value: TRIG_PP=403. This last casecorresponds to the horizontal straight line C₂ illustrated in FIG. 4,which intersects the Y-axis at the threshold value TRIG_PP=403.

Table I placed at the end of the description illustrates these twohypotheses and the results obtained concerning the probability ofdetection of the different sensor faults. This shows that forTRIG_PP=403 less than 1% of the cases of faults caused by thedisconnection of S₁ is not detected.

FIG. 4 shows an area Z₂ which is delimited by two straight lines C₃₁ andC₃₂ with negative gradients, situated on both sides of the straight lineC₃ corresponding to the aforementioned function (3). This area Z₂represents an area of safety for threshold margins which assure 100%detection of the faults caused by the sensors. More specifically, thestraight line C₃₂ assures a minimum threshold according to thetemperature T which makes it possible to assure this 100% detection. Thestraight line C₃₁ makes it possible to limit the maximum thresholdvalues to acceptable values, which are as low as possible. It is foundthat the straight line C₂ is outside the safety margin defined by thearea Z₂ for the low temperatures (range between −50° C. and +50° C.approximately), which explains why certain faults are not detected (lessthan 1%) as previously stated.

When the rotation speed state is E_(vt)>0, it is necessary to determinewhether the equation (B) is confirmed (“TRUE” logic state). The equation(B) is confirmed if the two inequations which constitute it areconfirmed simultaneously (“AND” logic function). In this equation, thethreshold parameter TRIG_PP no longer plays a part, and it isunnecessary to have temperature information.

On the other hand, it is necessary to know two other threshold values,i.e. V_(ref) and Δ.

The aforementioned threshold values depend in particular on the offsetvalues used (FIG. 2: circuits 332 and 33) in order to generate thesignals S_(sin) and S_(cos) (FIG. 2: outputs 300 and 310).

For the sake of clarity, according to an embodiment of the system 1 inFIG. 2, with numerical values on 10 bits, it is possible to adopt thefollowing typical values: Δ=43 and V_(ref)=512. When thresholds of thistype are adopted, experience shows that 100% of the disconnections ofthe three sensors S₁ to S₃ are detected.

According to an additional embodiment which is not specificallyillustrated, it is possible to refine further the diagnosis offunctioning faults of the angular position measurement sensors for therotor. This objective can be achieved by increasing the number of pairsof signals derived by means of linear combinations from the signalsgenerated by these sensors.

By reading the preceding description, it can easily be seen that theinvention achieves the objectives set: which need not be repeated infull.

In particular, as previously stated, the method according to theinvention makes it possible to carry out simply diagnosis of the mainfunctioning faults of the angular position measurement sensors for therotor, with great reliability, and without needing a significantincrease in the complexity of the circuits which are necessary forimplementation of this method. In fact, it is integrated perfectly inthe architectures of systems for angular position measurements for therotor according to the prior art, and requires only slight hardwareand/or software modifications, which does not lead to a significantadditional cost.

However, the invention is not limited simply to the method and deviceaccording to the invention explicitly described in relation to FIGS. 2to 4, or simply to the preferred application relating to determinationof the angular position of the rotor of a three-phase alternatorstarter.

Without departing from the context of the invention, the device appliesto any polyphase rotary machine, for example which is two-phase,three-phase, hexaphase, etc., in engine and/or alternator mode,comprising sensors for measurement of the angular position of the rotorrelative to the stator, and for which there is at least one pair ofsignals which are dephased in a non-trivial manner, and are obtained bylinear combinations of the polyphase signals generated by these sensors.

TABLE I Constant threshold TRIG_PP =403 =409 Faults % of non-detection %of non-detection No fault 0.0% 0.0% S₁ = 0 0.0% 0.0% S₁ = 5 0.0% 0.0% S₁disconnected 0.97% 0.0% S₂ = 0 0.0% 0.0% S₂ = 5 0.0% 0.0% S₂disconnected 0.0% 0.0% S₁ and S₂ = 0 0.0% 0.0% S₂ and S₃ = 0 0.0% 0.0%S₁ and S₂ disconnected 0.0% 0.0% S₁ and S₂ short-circuited 0.0% 0.0%

1. Method for diagnosis of functioning faults which exist in sensorsimplemented in a system for measurement of the angular position of arotor of a polyphase rotary electrical machine comprising a stator, thesensors being fixed relative to the stator, and able to detect amagnetic field and provide first signals which are representative ofthis magnetic field, characterised in that it comprises at least onestep of generating from linear combinations of the said first signals(101-103), at least one pair of first (200) and second (201) sinusoidalsignals, which are dephased by a predetermined value different from zeroand from 180°, representing an angular position of the rotor;determining a first parameter known as the speed state E_(vt) of therotor, which assumes two values E_(vt)>0 or E_(vt)≧0, calculating thefollowing first and second equations:−[(S _(pp)<TRIG_(—) PP) OR (C _(pp)<TRIG_(—) PP)];−[(V _(ref) −Δ<S<V _(ref)+Δ) AND [(V _(ref) −Δ<C<V _(ref)+Δ)], in which“OR” is the non-exclusive disjunction logic operator and “AND” is theconjunction logic operator, S_(pp) is the maximum peak-to-peak amplitudeand S is the instantaneous value of the said first sinusoidal signal(200). C_(pp) is the maximum peak-to-peak amplitude and C is theinstantaneous value of the said second sinusoidal signal (201), andTRIG_PP, V_(ref) and Δ are three predetermined threshold values;determining, when the said speed parameter E_(vt) is greater than zero,of the logic state “TRUE” or “FALSE” of said first equation, andgenerating a signal (400) which indicates fault-free functioning of thesaid sensors when this first equation is not confirmed, and afunctioning fault of at least one of these sensors when it is confirmed;and determining when the said speed state parameter E_(vt) is equal to,or greater than zero, the logic state “TRUE” or “FALSE” of the saidsecond equation, and generating a signal (400) which indicatesfault-free functioning of the said sensors when this second equation isnot confirmed, and a functioning fault of at least one of these sensorswhen it is confirmed.
 2. Method according to claim 1, characterised inthat it comprises a first, preliminary phase, which is carried outduring the design of the said system (1), for measurement of angularposition, comprising a step of constructing a mathematical model of saidsystem, a step of application to this model of a plurality of randommodifications according to a statistical method known as the Monte-Carlomethod, such as to obtain a distribution of states known as Boltzman'sdistribution, when a stationary state is reached, and of determiningsaid predetermined threshold value TRIG_PP on the basis of saiddistribution.
 3. Method according to claim 1, characterised in that saidsystem (1) for measurement of the position comprises a chain (7) forcalculation of the angular position, comprises an analogue-digitalconverter and circuits (32-33) which apply offset values to said first(200) and second (201) sinusoidal signals, it comprises a secondpreliminary phase which is carried out during the design of said system(1) for measurement of the angular position, comprising a step fordetermination of said predetermined threshold values V_(ref) and Δ, onthe basis of the said offset values and electrical characteristics ofsaid analogue-digital converter.
 4. Method according to claim 1,characterised in that it comprises a further step of acquisition of aspeed profile parameter of said system (1) for measurement of theangular position of a rotor, and a step for calculating on the basis ofsaid speed profile, of a minimum period of time which makes it possibleto carry out significant peak-to-peak measurements of the said first andsecond sinusoidal signals outside a transitory period.
 5. Methodaccording to one of claim 1, characterised in that, with said polyphaserotary electrical machine comprising a magnetic material which isinsensitive to temperature variations in a predetermined functioningrange of the said system (1) for measurement of the angular position ofthe rotor, the said threshold TRIG_PP is set to a constant minimum value(C₂) such as to delimit two regions, including a first region for valueshigher than said threshold, which is characteristic of fault-freefunctioning of said sensors (10), and a second region for values whichare lower than said threshold, which is characteristic of functioningfaults of said sensors (10).
 6. Method according to one of claim 1,characterised in that, with said polyphase rotary electrical machinecomprising a magnetic material which is sensitive to temperaturevariations in a predetermined functioning range of the said system (1)for measurement of the angular position of the rotor, it comprises astep of measurement or estimation of the temperature (42) of saidmagnetic material, and a step comprising making said threshold TRIG_PPdependent on the temperature, such as to have a linear function with theform TRIG_PP=pT+K_(s), where p is the gradient of the straight line (C₃)which represents this linear function, T is the temperature, and K_(s)is a constant, such as to delimit two regions, including a first regionfor values situated above said straight line (C₃), characteristic offault-free functioning of the said sensors (10), and a second region forvalues situated below said straight line (C₃), characteristic offunctioning faults said sensors (10).
 7. Device for implementation of amethod for diagnosis of functioning faults which exist in sensorsimplemented in a system for measurement of the angular position of arotor of a polyphase rotary electrical machine comprising a stator, thesensors being fixed relative to the stator, and able to detect amagnetic field and provide first signals which are representative ofthis magnetic field, characterised in that said device comprises means(41) for measurement of a speed of said rotor, and generation of asignal which is representative of a speed state E_(vt), an electronicdiagnostic module (40) which receives at least a first (200) and second(201) sinusoidal signals at first (e₁) and second (e₂) inputs, and asignal which represents said speed state E_(vt) at a third input (e₃),said diagnostic module (40) comprising means for development, on thebasis of these signals and said predetermined thresholds, of said firstand second equations, in order to confirm the “TRUE” or “FALSE” logicstates of these equations, and to generate as output (400) a signalwhich is representative of fault-free functioning of the said sensors(10), or of functioning faults of at least one of said sensors (10)according to the logic states.
 8. Device according to claim 7,characterised in that said polyphase rotary electrical machine comprisesa magnetic material which is sensitive to temperature variations in apredetermined functioning range of said system (1) for measurement ofthe angular position of the rotor, and also comprises means (42) formeasurement or estimation of the temperature of this material whichprovide a signal (T) representative of this temperature which istransmitted to a fourth input (e₄) of said diagnostic module (40), andin that this diagnostic module (40) generates a threshold value TRIG_PPwhich conforms with a linear function with the form TRIG_PP=pT+K_(s),where p is the gradient of the straight line which represents saidlinear function, T is the temperature, and K_(s) is a constant. 9.Device according to claim 7 characterised in that, since said polyphaserotary electrical machine is a three-phase machine, said system (1) formeasurement of the angular position of the rotor comprises three sensors(10) known as S₁ to S₃ respectively, in that it additionally comprisesmeans (100) for supply of electrical energy to said sensors (10) whichprovide a voltage V_(cc) with a predetermined amplitude, and in thatwhen said first equation is confirmed, said device generates as output(400) a diagnostic signal which indicates a type of fault includedamongst the following categories: the sensor S₁ is short-circuitedwhilst being connected to a predetermined potential (0V or V_(cc)), thesensor S₁ is disconnected, the sensors S₂ or S₃ are short-circuitedwhilst being connected to a predetermined potential (0V or V_(cc)) or toone another, the sensors S₁ and (S₂ or S₃) are disconnected, the sensorsS₁ and S₂ and S₃ are short-circuited whilst being connected to apredetermined potential (0V or V_(cc)) or to one another, the sensors S₁and S₂ and S₃ are disconnected or the said electrical energy supplymeans (100) are faulty.
 10. Device according to claim 7, characterisedin that, since said polyphase rotary electrical machine is a three-phasemachine, said system for measurement of the angular position of therotor comprises three sensors (10) known as S₁ to S₃ respectively, inthat it additionally comprises means (100) for supply of electricalenergy to the said sensors (10) which provide a voltage V_(cc) with apredetermined amplitude, and in that, when said second equation isconfirmed, said device generates as output (400) a diagnostic signalwhich indicates a type of fault included amongst the followingcategories: the sensors S₁ and S₂ and S₃ are disconnected, the sensorsS₁ and S₂ and S₃ are short-circuited whilst being connected to apredetermined potential (0V or V_(cc)), the sensors S₁ and S₂ and S₃ areshort-circuited whilst being connected to a predetermined potential (0Vor V_(cc)) or to one another, or said electrical energy supply means(100) are faulty.
 11. Device according to claim 7, characterised in thatsaid sensors (10) are constituted by Hall-effect sensors.
 12. Deviceaccording to claim 7, characterised in that said polyphase rotaryelectrical machine is an alternator-starter.
 13. Device according toclaim 7, characterised in that said diagnostic module (40) isconstituted by an on-board digital computer with a pre-recordedprogramme.